Trichogin GA IV: A versatile template for the synthesis of novel peptaibiotics

Abstract

Trichogin GA IV, isolated from the fungus Trichoderma longibrachiatum, is the prototype of lipopeptaibols, the sub-class of short-length peptaibiotics exhibiting membrane-modifying properties. This peptaibol is predominantly folded in a mixed 3(10)-/α- helical conformation with a clear, albeit modest, amphiphilic character, which is likely to be responsible for its capability to perturb bacterial membranes and to induce cell death. In previous papers, we reported on the interesting biological properties of trichogin GA IV, namely its good activity against Gram positive bacteria, in particular methicillin-resistant S. aureus strains, its stability towards proteolytic degradation, and its low hemolytic activity. Aiming at broadening the antimicrobial activity spectrum by increasing the peptide helical amphiphilicity, in this work we synthesized, by solution and solid-phase methodologies, purified and fully characterized a set of trichogin GA IV analogs in which the four Gly residues at positions 2, 5, 6, 9, lying in the poorly hydrophilic face of the helical structure, are substituted by one (position 2, 5, 6 or 9), two (positions 5 and 6), three (positions 2, 5, and 9), and four (positions 2, 5, 6, and 9) Lys residues. The conformational preferences of the Lys-containing analogs were assessed by FT-IR absorption, CD and 2D-NMR techniques in aqueous, organic, and membrane-mimetic environments. Interestingly, it turns out that the presence of charged residues induces a transition of the helical conformation adopted by the peptaibols (from 3(10)- to α-helix) as a function of pH in a reversible process. The role played in the analogs by the markedly increased amphiphilicity was further tested by fluorescence leakage experiments in model membranes, protease resistance, antibacterial and antifungal activities, cytotoxicity, and hemolysis. Taken together, our biological results provide evidence that some of the least substituted among these analogs are good candidates for the development of new membrane-active antimicrobial agents.

Partial thioamide scan on the lipopeptaibiotic trichogin GA IV. Effects on folding and bioactivity

“…In our view, it is risky to attempt to extract any conclusive conformational information from the CD properties of these three isomeric peptides between 195 and 250 nm because, in addition to the expected Cotton effects of the peptide chromophores [57–58], the thioamide chromophore [34–35] is also known to contribute heavily in this spectral region. However, we can safely state that the shape of the CD spectrum of the [Leu 11 -OMe] trichogin GA IV prototypical peptide [50,59] is most closely paralleled by that of its ψ[CS-NH] 5 analogue, although the former is significantly more intense. This finding is not surprising in view of the above-mentioned low influence of the thioamide chromophore on the spectrum of this monothionated compound.…”

“…Peptides Boc-Ile-Leu-OMe [66], Z-Leu-Aib-OMe [67], Z-Leu-Aib-O t -Bu [68], Boc-Gly-Leu-Aib-OMe [69], Boc-Gly-Ile-Leu-OMe [66], Boc-Leu-Aib-Gly-Ile-Leu-OMe [66], Boc-Gly-Gly-Leu-Aib-Gly-Ile-Leu-OMe [66], Z-Gly-Gly-Leu-Aib-O t -Bu [59], and Z-Aib-Gly-Leu-Aib-Gly-Gly-Leu-Aib-O t -Bu [59] are known compounds. Chemical characterizations and selected NMR spectra for the other peptides reported in Schemes 1–3 are given in Supporting Information File 1.…”

Alamethicin Supramolecular Organization in Lipid Membranes from 19F Solid-State NMR

“…These observations show that Gln 7 (and also Gly 11 and Pro 14 ) are not absolutely required for ion channel formation. Finally, it is worthwhile to mention that at high concentrations of ALM and independently of transmembrane potentials, bulky ions (e.g., N a -benzoyl-L-argininepara-nitroanilide and carboxyfluorescein) are able to pass the membrane (19)(20)(21).…”

Building Supramolecular DNA‐Inspired Nanowires on Gold Surfaces: From 2D to 3D

“…Film 2 has an additional non-covalently linked layer:a nu ndecapeptide analogue of the trichogin GA IV peptide [20] (defined hereafter as T-Tr(Lys)-A), in which the four glycine residues were replaced by four lysine residues to favour ahelical conformation [21] (Supporting Information, Figure S1) and reduce conformational flexibility,and the two extremities were functionalized with thymine and adenine for binding of Lipo-A and T-ZnTPP,respectively.Experimental details on the synthesis of molecular components and the film depositions are provided in the Supporting Information. In film 1, two components are used:a denine linked to al ipoic acid (Lipo-A) to covalently bind the gold surface and ZnTPP linked to at hymine molecule (T-ZnTPP).…”